1. Field of the Invention
The present invention relates to a system for visible light communication. More particularly, the present invention relates to a protocol for a wireless Local Area Network (LAN) system using visible light communication regarding retransmission of data, and an apparatus using the same.
2. Description of the Related Art
Recent improvements in the luminous efficiency of Light Emitting Diodes (LEDs) and improvements in their manufacture have resulted in a significant decrease in their purchase price. As a result, LEDs have become popular in general lighting markets, including markets formerly catering to sales of fluorescent lamps and glow lamps, as well as special lighting markets including markets of portable devices, displays, vehicles, traffic lights, billboards, etc. In particular, white LED has already surpassed glow lamps in terms of luminous efficiency, and white LED products superior to fluorescent lamps have recently emerged.
Moreover, in the field of wireless communications, various factors (e.g. the exhaustion of RF bandwidth, interference possibilities between several wireless communication technologies, an increasing demand for communication security, advent of an ultra-high speed ubiquitous communication environment based on 4 G wireless technologies, etc.) have increased interest in visible-light wireless communication technologies complementary to RF technologies, and the improvements in LED technology has heightened such interest. Accordingly, research on visible-light wireless communication employing a visible light LED is now in progress by many enterprises and laboratories.
There is an expectation that in the near future fluorescent lamps and glow lamps currently being used for lighting in homes, offices, and public places will in all likely be replaced by LEDs having higher performance and longer life.
An advantage of LEDs is that if current applied to an LED used for lighting is modulated, the LED for lighting can also be utilized as a communication light source. That is, it is possible to broadcast and transmit data only through an LED for lighting, without adding an additional light source. A user operating a mobile terminal or a notebook computer in a place where LED lighting is present can perform wireless LAN-type data communication by using a visible-light wireless transmission/reception module.
Wireless visible light communication differs greatly from other wireless RF communications in that a user can visually identify a data transmission/reception process, and visible light (i.e. a transmission medium) is characterized by high directivity of a signal and short transmission/reception distance of data. Due to the directivity of a signal, when an object passes (interferes) between the light path of LEDs of an access point (AP) and a mobile node (MN), a signal cut-off phenomenon may occur, thereby causing momentary data transmission/reception failure. The worse the channel condition is, and the more frequently the obstacle appears, the more frequently the momentary data transmission/reception failure occurs.
Therefore, there is a need in the art to develop a scheme for immediately recognizing momentary data transmission/reception failure(s) and enabling unsuccessfully received data to be rapidly re-transmitted.